According to the LAPD, undercover officers from the department's Special Investigation Section witnessed the robbery of a cellphone store and then saw a group of men, including Long, get into a gold Pontiac.

The group was under surveillance because police suspected they were involved in a series of similar robberies in the area, officials said.

LAPD Dets. Donald Walthers and Jeff Nolte followed the car away from the scene of the alleged robbery and used a "standard manuever" to block the vehicle, police said.

"The detectives also used their vehicles for cover and identified themselves as police officers, ordering the suspects to surrender," according to an LAPD news release.

Police allege that at that point, Marquis Walker, an 18-year-old black man who was seated in the back of the car, pulled a gun and pointed it in the direction of the detectives. Walthers and Nolte each fired at the car.

The detectives shot Long, who was in the front passenger's seat, and he died shortly after he was taken to a hospital. They also critically wounded the driver, Quantesa Wiley, a 19-year-old black woman, and wounded Samuel Taylor, an 18-year-old black man who was in the back seat of the car.

Police said they recovered the gun from the scene.

The shooting, as well as the alleged assault with a deadly weapon on police officers, is under investigation by the LAPD Force Investigation Unit. Walther has served on the force for 19 years, and Nolte has served for more than 20 years, authorities said.

Walker, Wiley and Taylor were all arrested on suspicion of robbery/homicide and are being held in lieu of $1-million bail, police said.

-- Anthony Pesce

Updated on August 13: The Times' Joel Rubin reports today that Det. Jeff Nolte had been involved in a controversial shooting in 1997. In that incident, Nolte shot a drug suspect, who the city later paid $2 million in damages.